Beginning SQL

Chapter 3
Member Name
The member is called Jack Johnson
The member is called Seymour Botts
The member is called Susie Simons
The member is called Jamie Hills
The member is called Stuart Dales
The member is called William Doors
The member is called Doris Night
That completes the look at concatenation. The next section shows you how to select data from more than
one table at a time.
Selecting Data from More Than One Table
90
Using the SQL you’ve learned so far, you can extract data from only one table in the database, which is
quite limiting because often answers require data from more than one table. The developers of SQL realized
this limitation and implemented a way of joining data from more than one table into one results set.
Using the word joining is no accident: in SQL the JOIN keyword joins one or more tables together in a
results set. Chapter 8 examines all the different types of joins, but this chapter covers the most commonly
used (and also the easiest to use) join: the inner join.
To see why joins are necessary and useful, begin with a problem. Say that you want a list of all the film
names, years of release, and ratings for the Historical film category. Assume that you know the category
name but don’t know what the CategoryId value is for Historical.
If SQL didn’t support joins, your first task would be to look in the Category table for the CategoryId for
the category with a value Historical:
SELECT CategoryId
FROM Category
WHERE Category = ‘Historical’;
The preceding SQL returns just one result: 6. Now you know that the CategoryId for Historical is 6,
and that can be used with the CategoryId column in the Films table to get a list of films in the
Historical category:
SELECT FilmName, YearReleased, Rating
FROM Films
WHERE CategoryId = 6;
Running the preceding SQL returns the following results: